新型Ce掺杂MnO_(x)高效低温甲苯催化氧化性能

Novel Ce-doped MnO_(x) catalysts for highly efficient catalysis of toluene oxidation at low temperature

采用氧化-共沉淀方法制备新型Ce-MnO_(x)双金属氧化物催化剂,探究Ce,Mn活性组分间协同作用对甲苯低温催化性能的影响.通过SEM、XRD、N_(2)吸脱附曲线、XPS、EPR、H_(2)-TPR和in situ DRIFTS对催化剂物理及化学性能进行表征.结果表明,当Ce:Mn物质的量比为1:3时,CeMn_(3)O_(x)具有最低的甲苯催化温度及良好的稳定性和耐久性,且在215和233℃下分别实现甲苯的50%和90%催化,远低于MnO_(x)催化温度.表征结果证实,Ce的引入有利于调节CeMn_(3)O_(x)催化剂形成珊瑚形貌,降低催化剂结晶度形成晶相-非晶相界面,创造更多缺陷位点,提高氧空位浓度,调节氧种类促进O_(latt)←→O_(sur)←→O_(ads)的转换,增强还原性能.同时,in situ DRIFTS图谱证实了在有氧条件下,甲苯氧化遵循两条反应路径,Ⅰ:吸附→苯甲醇→苯甲醛→苯甲酸→苯酚→苯环C=C断裂→CO_(2)和H_(2)O,Ⅱ:吸附→苯环C=C断裂→环状酸酐→CO_(2)+H_(2)O两条反应路径,其中苯环C=C双键的断裂为控速步骤.

Novel Ce-doped MnO_(x) bimetallic catalyst was successfully prepared by co-oxidation-precipitation method,and the influence of synergy between Ce and Mn was explored for catalytic toluene oxidation at low temperature.Characterizations by SEM、XRD、N_(2) adsorption-desorption、XPS、EPR、H_(2)-TPR,and in situ DRIFTS were performed for the prepared catalysts.It is found that the catalysts with an optimum Ce/Mn molar ratios of 1:3 had a highest performance with T_(50) of 215℃ and T_(90) of 233℃,good durability and water resistance for the toluene oxidation.Meanwhile,the results confirmed that the introduction of Ce was beneficial to adjust the morphology of CeMn_(3)O_(x) catalyst with the formation of coral-structure,leading to the increase in the number of interfaces between crystalline-amorphous,which caused more defects and oxygen vacancies in the bulk of catalyst,promoting the conversion of O_(latt)←→O_(sur)←→O_(ads) and enhancing the reducibility.Finally,in situ DRIFTS spectra verified that toluene oxidation followed two reaction pathways under air conditions,Ⅰ:adsorption→benzyl alcohol→benzaldehyde→benzoate→phenol→benzene ring C=C breakage→CO_(2) and H_(2)O,Ⅱ:adsorption→benzene ring C=C cleavage breakage→Maleic anhydride→CO_(2) and H_(2)O,in which the C=C breakage of the aromatic ring was considered as a rate-controlled step.